Residual Ultimate Strength Analysis Of Cracked Ship Structures

Ship structure may be suffered from many types of damages during its service. Thefatigue damage is the main damage style, in addition to corrosion damage. Anexamination of the cracking damage position confirms a such fact that the damages oftenappear in welded joints and local areas of stress concentrations under the periodical loadand the crack may be accompanied with the ship whole life. Fatigue cracking was studiedbased on fracture mechanics theory. While it is also important to understand the effect of acrack on the collapse response of a cracked member under monotonic loading and henceto evaluate the reduction in ultimate strength. In the longer term this understanding isexpected to contribute in the formulation of standards to assess the structural integrity ofageing structures.In this thesis, a numerical study on the residual ultimate strength of ship structuressubjected to axial compressive is carried out. At first, numerical analyses on the ultimatestrength of perfect stiffened plates are investigated considering the effects of severalparameters such as flexible factor of plates, flexible factors of stiffened plates andcharacteristics of stiffeners. In addition, the residual ultimate strength reductioncharacteristics of plate elements and stiffened plates due to cracking damage areundertaken with varying size, shape and location of the cracking damage and varyingthickness and aspect ratio of the plate’s geometrical dimensions. And also, A series ofnonlinear finite element analyses for plate elements including two parallel cracks areperformed.At last, buckling problems of the ship structural details are also discussed, suchas the problem that the capacity of stiffeners will reduce because of buckling/plasticity. Bytaking the transverse section of the box-shape girder for the chemical tanker bulkhead,according to Smith method, the ultimate vertical bending moment of amidships is obtainedwith progress collapse analysis. The results of the numerical computations obtained aredocumented. The insights developed will be very useful for the ultimate limit state basedrisk or reliability assessment of aging steel plated structures with cracking damage.